Containment of molten aluminum using non-wetting materials

ABSTRACT

A method of containing molten aluminum using non-wetting materials comprising depositing MgAl 2 O 4 , or one selected from an oxide, Al 2 O 3 , nitride, AlN, BN, carbide, and SiC, onto a crucible. An apparatus for containment of molten aluminum using non-wetting materials comprising a layer of MgAl 2 O 4 , or one selected from an oxide, Al 2 O 3 , nitride, AlN, BN, carbide, and SiC, deposited onto a crucible.

REFERENCE TO RELATED APPLICATION

This application is a non-provisional of, and claims priority to and thebenefits of, U.S. Provisional Patent Application No. 61/770,742 filed onFeb. 28, 2013, the entirety of which is hereby incorporated byreference.

BACKGROUND

This disclosure pertains to a method and apparatus of containing moltenaluminum using a barrier layer of a non-wetting material.

Thermal evaporation is a very common method of depositing thin films ofaluminum. In this technique, aluminum shot is placed into a cruciblethat is typically made of graphite, a refractory metal, or an oxide, andheated using either an electron beam or resistive coils. Unfortunately,molten aluminum has a strong propensity to wet most crucible materialsand is highly corrosive to refractory metals, such as tungsten andmolybdenum. As the molten aluminum creeps during the deposition, it canwet out onto other system elements, solidify on the backside of thecrucible and cause thermal shock and cracking, corrode resistive heatingelements, and change the thermal conduction properties of the crucible.This problem is typically managed by frequently replacing crucibles,leading to excess cost and material waste.

SUMMARY OF DISCLOSURE Description

This disclosure pertains to a method and apparatus of containing moltenaluminum using a barrier layer of a non-wetting material.

DESCRIPTION OF THE DRAWINGS

The following description and drawings set forth certain illustrativeimplementations of the disclosure in detail, which are indicative ofseveral exemplary ways in which the various principles of the disclosuremay be carried out. The illustrated examples, however, are notexhaustive of the many possible embodiments of the disclosure. Otherobjects, advantages and novel features of the disclosure will be setforth in the following detailed description when considered inconjunction with the drawings.

FIG. 1: Illustration of a used Fabmate crucible with spinel-coated rims.Fabmate crucible with alternating bare and spinel-coated regions aroundthe rim after one aluminum deposition. Note the straight lines ofaluminum at the edge of the spinel film, indicating non-wettingbehavior.

FIG. 2: Illustration of a used Fabmate crucible without spinel-coatedrims. Fabmate crucible without spinel coating after one aluminumdeposition. The rim is entirely coated with aluminum, and it isbeginning to creep out of the crucible in one region.

DETAILED DESCRIPTION OF THE INVENTION

We discuss here a method to contain molten aluminum within a crucibleusing non-wetting barrier layers.

The non-wetting material is chosen to have a surface energy that resultsin a large contact angle (i.e. 90°) when in contact with moltenaluminum.

The non-wetting material can be deposited using a variety of methods.

As the molten aluminum wets out its container, the material is stoppedat the edge of the deposited material and will not advance further,prolonging crucible lifetime and reducing source material waste.

Additionally, while this initial disclosure references laboratory-scalecontainment, the technique is applicable to containers of any size andshape. This disclosure solves a real practical problem which affects thecommercial market.

Example 1

MgAl₂O₄ (spinel) was deposited using RF magnetron sputtering onto twoFabmate (densified graphite) crucibles with an energy density of ˜9W/cm² and a pressure of 1-10 mT with the crucibles held at roomtemperature for an estimated spinel film thickness of 500-1000 nm.

The crucibles were rotated at ˜10 rpm during deposition.

The crucibles were masked off using polyimide adhesive tape to confinethe deposited spinel to the rim of the crucible.

After deposition, the polyimide tape was removed and the crucibles werewiped clean using solvents.

Aluminum shot is added to the crucible, which is subsequently installedin a high vacuum electron beam evaporation chamber. The electron beam israstered in a Lissajous pattern to heat the aluminum, with care taken toavoid direct heating of the rim.

The crucible is heated to ˜1200° C., at which point aluminum reaches thedesired deposition rate.

We have found the method and apparatus as discussed herein extends thelifetime of crucibles.

Another advantage includes reduced waste from discarded source material.Furthermore, the method and apparatus as discussed herein reduces damagepotential from aluminum creep onto system components.

These advantages are demonstrated in the figures.

FIG. 2 illustrates a used Fabmate crucible without spinel-coated rims.The Fabmate crucible shown is without spinel coating after one aluminumdeposition.

Note the rim is entirely coated with aluminum, and it is beginning tocreep out of the crucible in one region.

This is in contrast to FIG. 1 which illustrates a used Fabmate cruciblewith spinel-coated rims. This Fabmate crucible has alternating bare andspinel-coated regions around the rim after one aluminum deposition.

Note the straight lines of aluminum at the edge of the spinel film,indicating non-wetting behavior.

Instead of MgAl₂O₄, a variety of other materials can be used, includingbut not limited to oxides, such as Al₂O₃, or nitrides, such as AN andBN, or carbides, such as SiC.

Instead of sputter deposition, other deposition methods can be used,such as chemical vapor deposition, thermal spray, or thermalevaporation, as well as dip coating or spray coating of precursorsfollowed by thermal treatment.

Furthermore, suitable coatings can also be used to prevent wetting byother metals and alloys.

The above examples are merely illustrative of several possibleembodiments of various aspects of the present disclosure, whereinequivalent alterations and/or modifications will occur to others skilledin the art upon reading and understanding this specification and theannexed drawings. In addition, although a particular feature of thedisclosure may have been illustrated and/or described with respect toonly one of several implementations, such feature may be combined withone or more other features of the other implementations as may bedesired and advantageous for any given or particular application. Also,to the extent that the terms “including”, “includes”, “having”, “has”,“with”, or variants thereof are used in the detailed description and/orin the claims, such terms are intended to be inclusive in a mannersimilar to the term “comprising”.

What we claim is:
 1. A method of containing molten aluminum usingnon-wetting materials comprising: masking off a crucible using a mask toconfine any deposition to the rim of the crucible; depositing MgAl₂O₄onto the crucible; and rotating the crucible during deposition.
 2. Themethod of containing molten aluminum using non-wetting materials ofclaim 1 further comprising the steps of; removing the mask from thecrucible; and cleaning the crucible using solvents.
 3. The method ofcontaining molten aluminum using non-wetting materials of claim 1wherein the step of depositing MgAl₂O₄ onto the crucible was via RFmagnetron sputtering.
 4. The method of containing molten aluminum usingnon-wetting materials of claim 3 wherein the RF magnetron sputtering wasat an energy density of ˜9 W/cm² and a pressure of 1-10 mT and whereinthe crucible was held at room temperature for an estimated spinel filmthickness of 500-1000 nm.
 5. The method of containing molten aluminumusing non-wetting materials of claim 4 wherein the step of rotating thecrucible during deposition was at ˜10 rpm during deposition.
 6. Themethod of containing molten aluminum using non-wetting materials ofclaim 5 wherein the MgAl₂O₄ is substituted for one selected from thegroup consisting of oxides, Al₂O₃, nitrides, AlN, BN, carbides, and SiC.7. An apparatus for containment of molten aluminum using non-wettingmaterials comprising: a crucible; a layer of MgAl₂O₄ deposited onto thecrucible; and wherein said layer of MgAl₂O₄ is deposited near the rim ofthe crucible.
 8. The apparatus for containment of molten aluminum usingnon-wetting materials of claim 7 wherein the layer of MgAl₂O₄ has athickness of at least 500 nm.
 9. The apparatus for containment of moltenaluminum using non-wetting materials of claim 7 wherein the layer ofMgAl₂O₄ is substituted for one selected from the group consisting ofoxides, Al₂O₃, nitrides, AlN, BN, carbides, and SiC.